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Nov 27, 2016
11/16

Nov 27, 2016
by
René van Bevern; Robert Bredereck; Morgan Chopin; Sepp Hartung; Falk Hüffner; André Nichterlein; Ondřej Suchý

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Finding the origin of short phrases propagating through the web has been formalized by Leskovec et al. [ACM SIGKDD 2009] as DAG Partitioning: given an arc-weighted directed acyclic graph on $n$ vertices and $m$ arcs, delete arcs with total weight at most $k$ such that each resulting weakly-connected component contains exactly one sink---a vertex without outgoing arcs. DAG Partitioning is NP-hard. We show an algorithm to solve DAG Partitioning in $O(2^k \cdot (n+m))$ time, that is, in linear...

Topics: Discrete Mathematics, Data Structures and Algorithms, Computing Research Repository, Social and...

Source: http://arxiv.org/abs/1611.08809

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Nov 25, 2016
11/16

Nov 25, 2016
by
Andreas Ammon; Alan Genz; Tobias Hartung; Karl Jansen; Hernan Leövey; Julia Volmer

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The error scaling for Markov-Chain Monte Carlo techniques (MCMC) with $N$ samples behaves like $1/\sqrt{N}$. This scaling makes it often very time intensive to reduce the error of computed observables, in particular for applications in lattice QCD. It is therefore highly desirable to have alternative methods at hand which show an improved error scaling. One candidate for such an alternative integration technique is the method of recursive numerical integration (RNI). The basic idea of this...

Topic: High Energy Physics - Lattice

Source: http://arxiv.org/abs/1611.08628

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Oct 6, 2016
10/16

Oct 6, 2016
by
Andreas Ammon; Tobias Hartung; Karl Jansen; Hernan Leövey; Julia Volmer

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In lattice Quantum Field Theory, we are often presented with integrals over polynomials of coefficients of matrices in U(N) or SU(N) with respect to the Haar measure. In some physical situations, e.g., in presence of a chemical potential, these integrals are numerically very difficult since their integrands are highly oscillatory which manifests itself in form of the sign problem. In these cases, Monte Carlo methods often fail to be adequate, rendering such computations practically impossible....

Topic: High Energy Physics - Lattice

Source: http://arxiv.org/abs/1610.01931

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Jul 27, 2016
07/16

Jul 27, 2016
by
Sebastian Andres; Lisa Hartung

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We construct a class of one-dimensional diffusion processes on the particles of branching Brownian motion that are symmetric with respect to the limits of random martingale measures. These measures are associated with the extended extremal process of branching Brownian motion and are supported on a Cantor-like set. The processes are obtained via a time-change of a standard one-dimensional reflected Brownian motion on $\mathbb{R}_+$ in terms of the associated positive continuous additive...

Topics: Probability, Mathematics

Source: http://arxiv.org/abs/1607.08132

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Jul 18, 2016
07/16

Jul 18, 2016
by
A. Ammon; T. Hartung; K. Jansen; H. Leövey; J. Volmer

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In this paper we describe a new integration method for the groups $U(N)$ and $SU(N)$, for which we verified numerically that it is polynomially exact for $N\le 3$. The method is applied to the example of 1-dimensional QCD with a chemical potential. We explore, in particular, regions of the parameter space in which the sign problem appears due the presence of the chemical potential. While Markov Chain Monte Carlo fails in this region, our new integration method still provides results for the...

Topics: Numerical Analysis, High Energy Physics - Lattice, Mathematics

Source: http://arxiv.org/abs/1607.05027

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Jun 23, 2016
06/16

Jun 23, 2016
by
S. Eckart; M. Richter; M. Kunitski; A. Hartung; J. Rist; K. Henrichs; N. Schlott; H. Kang; T. Bauer; H. Sann; L. Ph. H. Schmidt; M. Schöffler; T. Jahnke; R. Dörner

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We report on non-sequential double ionization of Ar by a laser pulse consisting of two counter rotating circularly polarized fields (390 nm and 780 nm). The double ionization probability depends strongly on the relative intensity of the two fields and shows a "knee"-like structure as function of intensity. We conclude that double ionization is driven by a beam of nearly monoenergetic recolliding electrons, which can be controlled in intensity and energy by the field parameters. The...

Topics: Atomic Physics, Physics

Source: http://arxiv.org/abs/1606.07303

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Apr 5, 2016
04/16

Apr 5, 2016
by
Robert J. De Rosa; Julien Rameau; Jenny Patience; James R. Graham; René Doyon; David Lafrenière; Bruce Macintosh; Laurent Pueyo; Abhijith Rajan; Jason J. Wang; Kimberly Ward-Duong; Li-Wei Hung; Jérôme Maire; Eric L. Nielsen; S. Mark Ammons; Joanna Bulger; Andrew Cardwell; Jeffrey K. Chilcote; Ramon L. Galvez; Benjamin L. Gerard; Stephen Goodsell; Markus Hartung; Pascale Hibon; Patrick Ingraham; Mara Johnson-Groh; Paul Kalas; Quinn M. Konopacky; Franck Marchis; Christian Marois; Stanimir Metchev; Katie M. Morzinski; Rebecca Oppenheimer; Marshall D. Perrin; Fredrik T. Rantakyrö; Dmitry Savransky; Sandrine Thomas

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We present new $H$ (1.5-1.8 $\mu$m) photometric and $K_1$ (1.9-2.2 $\mu$m) spectroscopic observations of the young exoplanet HD 95086 b obtained with the Gemini Planet Imager. The $H$-band magnitude has been significantly improved relative to previous measurements, whereas the low resolution $K_1$ ($\lambda/\delta\lambda \approx 66$) spectrum is featureless within the measurement uncertainties, and presents a monotonically increasing pseudo-continuum consistent with a cloudy atmosphere. By...

Topics: Earth and Planetary Astrophysics, Astrophysics

Source: http://arxiv.org/abs/1604.01411

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Mar 15, 2016
03/16

Mar 15, 2016
by
J. R. Calvey; W. Hartung; J. Makita; M. Venturini

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The buildup of low energy electrons in an accelerator, known as electron cloud, can be severely detrimental to machine performance. Under certain beam conditions, the beam can become resonant with the cloud dynamics, accelerating the buildup of electrons. This paper will examine two such effects: multipacting resonances, in which the cloud development time is resonant with the bunch spacing, and cyclotron resonances, in which the cyclotron period of electrons in a magnetic field is a multiple...

Topics: Accelerator Physics, Physics

Source: http://arxiv.org/abs/1603.04817

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Jan 26, 2016
01/16

Jan 26, 2016
by
Schuyler G. Wolff; Marshall Perrin; Maxwell A. Millar-Blanchaer; Eric L. Nielsen; Jason Wang; Andrew Cardwell; Jeffrey Chilcote; Ruobing Dong; Zachary H. Draper; Gaspard Duchene; Michael P. Fitzgerald; Stephen J. Goodsell; Carol A. Grady; James R. Graham; Alexandra Z. Greenbaum; Markus Hartung; Pascale Hibon; Dean C. Hines; Li-Wei Hung; Paul Kalas; Bruce Macintosh; Franck Marchis; Christian Marois; Laurent Pueyo; Fredrik T. Rantakyro; Glenn Schneider; Anand Sivaramakrishnan; Sloane J. Wiktorowicz

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We present H and K band imaging polarimetry for the PDS 66 circumstellar disk obtained during the commissioning of the Gemini Planet Imager (GPI). Polarization images reveal a clear detection of the disk in to the 0.12'' inner working angle (IWA) in H band, almost 3 times as close to the star as the previous HST observations with NICMOS and STIS (0.35'' effective IWA). The centro-symmetric polarization vectors confirm that the bright inner disk detection is due to circumstellar scattered light....

Topics: Earth and Planetary Astrophysics, Astrophysics

Source: http://arxiv.org/abs/1601.07248

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Jan 13, 2016
01/16

Jan 13, 2016
by
S. Zeller; M. Kunitski; J. Voigtsberger; A. Kalinin; A. Schottelius; C. Schober; M. Waitz; H. Sann; A. Hartung; T. Bauer; M. Pitzer; F. Trinter; C. Goihl; C. Janke; M. Richter; G. Kastirke; M. Weller; A. Czasch; M. Kitzler; M. Braune; R. E. Grisenti; W. Schöllkopf; L. Ph. H. Schmidt; M. Schöffer; J. B. Williams; T. Jahnke; R. Dörner

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We report on coulomb explosion imaging of the wavefunction of the quantum halo system He$_2$. Each atom of this system is ionized by tunnelionization in a femto second laser pulse and in a second experiment by single photon ionization employing a free electron laser. We visualize the exponential decay of the probability density of the tunneling particle over distance for over two orders of magnitude up to an internuclear distance of 250 {\AA}. By fitting the slope of the density in the...

Topics: Atomic Physics, Nuclear Experiment, Atomic and Molecular Clusters, Chemical Physics, Physics

Source: http://arxiv.org/abs/1601.03247